Study of Radiative Deexcitation Processes in the Muonic Helium(4) Ion at 14 and 40 Atmospheres

To search for a long living 2S1/2 state in the muonic helium ion at helium gas pressures of 14 and 40 atmospheres, radiative muon transitions were registered in a time resolved mode using sodium iodide crystals. Special care was taken to avoid gas impurities which are known to reduce the 2s lifetime significantly. In addition to the prompt photons of the K-series, a delayed component was detected. The lifetime and yield of this component agree with theoretical values for ions not perturbed by the surrounding medium. However, test measurements carried out with other target gases clearly demonstrate that practically all of the delayed events observed in pure helium are not caused by the radiative decay of a longliving 2s state.